Heating cables are commonly used in bathroom floors, where they are exposed to a very aggressive environment with high humidity and high values of pH.
The main problem with such heating cables is that humidity can enter the cable end from the inside. This may be due to a damage on the outer cable sheath or water from the outside (e.g. from surrounding concrete). Water that has penetrated to the cable end seal can create an electrical bridge between the phase conductor element and the earth screen or wire in the cable, and the product fails. Typically this will occur a short time after installation, and there may be large direct costs for repairing the damage.
It is also a tendency that the insulation of the resistance wire after some time with heat cycling will retract, with the consequence that the metal in the phase conductor element comes in direct contact with the earth wire. This is called “shrink-back of insulation” and is typically something that happens after the heating cable has been installed and has been operating for some time. The main reason for this is bad adherence between the conductor and the insulation (e.g. cross-linked polyethylene insulation) applied thereto.
It is known to use different techniques as e.g. combinations of: shrink sleeves, hot-melt glues, or shrink sleeves with glue combined with an end-cap welded to the cable outer sheath, to both insulate the end portions of the electrical conductors and to seal off the cable end against water penetration. Experience shows that this method is not always satisfactory. Water may in some cases penetrate the end seal and form an electrical bridge from the conductor connection to the earth wire.
Another prior solution comprises a shrink hose with glue as electrical insulation (giving an inner seal) and an end-cap, preferably of a PVC material, welded on to give an outer seal. However, this solution has weakness in that it is not waterproof in 100% of the cases. Some quality variations in the level of shrinking may occur. In addition the manufacturing process with a crimp hose and a PVC end-cap is very time-consuming, and relatively expensive parts are needed.